As a piezoelectric vibrator used in oscillation devices, bandpass filters, and the like, a crystal vibrator that uses thickness shear vibration is widely used. As such a crystal vibrator, for example, a crystal vibrator having a mesa-structure is known in which, in order to confine the vibration energy of thickness shear vibration, an etching process is performed so as to make a center portion of the crystal vibrator thicker than a peripheral portion of the crystal vibrator and drive electrodes are formed on both main surfaces of the center portion (Patent Document 1). Accordingly, because it is possible to concentrate more vibration energy directly under the drive electrodes, it is possible to make the crystal impedance value (CI value) lower than that of a crystal vibrator having a simple flat shape and to improve the electrical characteristics.
However, in the existing mesa-structure, there have been cases where vibration energy that occurs at the vibration portion and vibration energy of unnecessary vibration that occurs by reflection of vibration at an end surface of an outer peripheral portion at the periphery of the vibration portion become mixed and the characteristics of the crystal vibrator deteriorate. Moreover, reflection of vibration may occur at an end surface or corner where the thickness changes between a region of the center portion and the peripheral portion, and there is a possibility of spurious vibration, which is unnecessary vibration, increasing. Moreover, extending electrodes that extend from the drive electrodes may become disconnected in the vicinity of a corner of a step portion formed at the boundary between the center portion and the peripheral portion. In addition, stress concentrates in the vicinity of the corner of the step portion and, for example, there is a possibility of cracks occurring at the time of mounting the crystal vibrator or the like.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-53820